The present invention relates to a composite metallic wire which can be suitably used as a coil wire for a composite type magnetic head, particularly, as a coil wire for a high-density magnetic recording head and to a magnetic head using the composite metal wire.
With the spread of computers, an increase of a capacity and a speed up of a magnetic recording apparatus have been rapidly improving. Accordingly, a magnetic head is required to have (1) a smaller size and (2) a lower inductance.
In order to enlarge a valid recording area and improve a running followability of a magnetic recording apparatus, a slider is changed from one having dimensions of 4.3 mm.times.2.9 mm.times.0.86 mm, which was a standard slider originally, to another one having dimensions of 2.0 mm.times.1.6 mm.times.0.46 mm, which is a main current slider and called "50% slider". Further, a slider called "30% slider" is under investigation.
In order to improve a transmitting speed, it is required to use a high frequency upon reproducing a record. Therefore, it is required that an inductance of a magnetic head is lowered so as to shorten a rise time of a recording current in a range of high frequencies. For example, in the case of 600 Mb/in.sup.2, the inductance is required to be 0.9 .mu.H or less. In the case of 700 Mb/in.sup.2, the inductance is required to be 0.7 .mu.H or less. For reducing an inductance of a magnetic head, it is required that a cross sectional area of a magnetic path is reduced, for example, a thickness of a magnetic core is reduced, thereby causing a problem of reducing an efficiency of the head. To solve the problem, a magnetic path should be shortened. Specifically, a window for a coil should be made smaller, thereby reducing an inductance.
However, a window for a coil of a magnetic core is required to be wound by a coil wire with a predetermined number of turns. For example, in the case of 600 Mb/in.sup.2, the number is 26, and in the case of 700 Mb/in.sup.2, the number is 24. Therefore, the window is required to have a size sufficient for the winding. Accordingly, a minimum size of the window for a coil depends on a diameter of a wire used for the coil.
FIG. 3 shows a core chip in which a conventional wire is used. The core chip 10 mainly consisting of a trailing core 16 and leading core 18. A coil 28 made of a wire is wound around a window 12 for a coil formed by the trailing core 16 and a leading core 18.
The surfaces of the trailing core 16 and the leading core 18 which are facing to each other are covered with metallic films 22, respectively. Between these films, a magnetic gap 20 consisting of a glass 24 is formed. Incidentally, 26 is an insulating protective tube.
As shown in FIG. 3, a conventional core chip in which a wire is used, the coil has a large diameter. Accordingly, the window 12 for a coil could not be made smaller, and inductance could not be reduced.
Conventionally, an alloy of copper and silver has been used as a material for the wire having a minimum diameter of 22 .mu.m and a maximum tensile strength of 20 g.
It is technically possible to thin down a copper alloy wire conventionally used. However, indeed, a wiring operation is manual, and therefore, a wire having a low tensile strength has problems of the snapping of the wire, and the like. Accordingly, the wire is required to have a tensile strength of at least 20 g. Therefore, it is difficult to use a thin copper alloy wire as a coil wire from the view point of mass-production.
Accordingly, it is difficult to achieve a memory density of 600 Mb/in.sup.2 or more by using a magnetic head using a wire such as a conventional copper alloy wire.
As a structure of a composite type magnetic head, a core chip embedding type is known.
For producing this magnetic head, a track machining is first given, a core chip having a thickness (d) of 50 .mu.m is inserted into a groove for inserting a core chip and tentatively fixed. Then, glass is fused and poured in the periphery of the track portion so as to fix the core chip to the slider. After that a tentative fixing member in a back portion is removed, and a resin is poured into the portion to fix the core chip to the slider. Then, surplus glass on a sliding surface is removed, and simultaneously, the surface is polished so as to form a gap depth.
A composite type magnetic head thus produced has a structure shown in, for example, FIG. 4.
In FIG. 4, 30 is a non-magnetic housing. In a condition that a core chip 29 is fixed to the housing 30, a coil 31 is set so as to form a slider 36. To the slider 36 having a coil 31 is connected a suspension 32 for generating a force toward a medium. To the suspension is fixed a tube 33 for insulating and protecting a lead wire 35. In this condition, a magnetic head 37 is constituted.
The magnetic head 37 floats at a minute intervals on the medium by a balance of a floating force and a pressure from the slider 36 to the medium by the suspension 32. The floating force is generated between a sliding surface and the medium. Thus, the magnetic head 37 can move over the medium of the slider 36 at a high speed.
The smaller and lighter slider 36 is more preferable because a flowability is enhanced against a rough surface of the medium, the floating is more stable, a magnetic converting property is enhanced, and a speed-up of the movement of the slider 36 over the medium can be achieved. However, a size of the slider 36 is restricted by a size of a slit 34. As seen from FIG. 4, since a wire is wound in a state that the slider 36 slides, the slider 36 is provided with a slit 34 for the winding. A size of the slit 34 is restricted by a size of a slider 36. A size of the slit 34 is a maximum restrictive matter in the case that a size of the slider 36 is decreased. Accordingly, making a wire material for a coil thinner and making the coil smaller enables to miniaturization of the slider 36, thereby improving a floating stability.
Thus, it is important to thin down a wire material for a coil in a composite type magnetic head, too.